Strange occurrence. I was forced to re-install Windows 8 after 8.1 became unstable. In doing so my 3TB is now only reading 2.0TB with 784 GB in unallocated.

I have played around with trying software convert from MBR back to GPT to no avail (AOMEI).

Any easier suggestion?

Bruce E

May 28, 2014 at 2:35 pm

If the system boots from from the installation media in UEFI mode, it will normally work without a hitch. Sometimes a system may not boot in UEFI mode though and the system works in a legacy BIOS mode which cannot boot from a GPT disk, so it gets partitioned as a MBR disk with its inherent limitations (partitions limited to 2.2TB; only 4 primary partitions).

It is also possible that the drive had existing partitions and the installer saw a MBR partition table on the drive, so it assumed it was supposed to keep the drive as MBR. I saw this once with a "hybrid MBR/GPT" drive which appears to be a Microsoft-only thing. By following the steps above, we are avoiding this scenario. Hovsep's instructions above should do the same thing, but I took the extra steps of creating all of the required partitions for Windows to boot from a GPT disk by creating the EFI partition, the Microsoft System Reserved partition, then the OS partition leaving no room for doubt for the installer.

Bruce E

May 27, 2014 at 5:41 am

I have not yet found any means of converting a system disk from MBR to GPT. Your only option would be to make a backup of everything you want to save, remove/disconnect all hard drives except the one you want to boot with, UEFI boot your Win8 media and at the initial installation screen, press Shift+F10 to get a command prompt, then prep your hard drive as a GPT drive for installation using diskpart by entering the following commands:
diskpart
select disk 0
clean
convert gpt
create partition efi size=100
format fs=fat32 quick label=system
create partition msr size=128
create partition primary size=#size of OS partition#
format fs=NTFS quick label=C
assign letter=c
exit
exit

Replace the #size of OS partition# with the size you wish to use (in MB).

At this point, resume the Win8 installation.

In order for all of this to work, your system MUST be using UEFI boot.

Ned Ruffin III

May 27, 2014 at 3:05 pm

"The eagle has landed!" Success is mine thanks to my wonderful support team!" All is now well and again thanks a bunch. Question though. I have normally re-done my system with the same setup (operating system is on a 500 GB drive and the 3TB is merely storage) and this is the first time this occurred. Any ideas of what may have gone awry?